A mobile observatory powered by sun and wind for near real time measurements of atmospheric, glacial, terrestrial, limnic and coastal oceanic conditions in remote off-grid areas

Climate change is rapidly altering the Arctic environment. Although long-term environmental observations have been made at a few locations in the Arctic, the incomplete coverage from ground stations is a main limitation to observations in these remote areas. Here we present a wind and sun powered multi-purpose mobile observatory (ARC-MO) that enables near real time measurements of air, ice, land, rivers, and marine parameters in remote off-grid areas. Two test units were constructed and placed in Northeast Greenland where they have collected data from cabled and wireless instruments deployed in the environment since late summer 2021. The two units can communicate locally via WiFi (units placed 25 km apart) and transmit near-real time data globally over satellite. Data are streamed live and accessible from (https://gios.org). The cost of one mobile observatory unit is c. 304.000€. These test units demonstrate the possibility for integrative and automated environmental data collection in remote coastal areas and could serve as models for a proposed global observatory system.

We found that during the summer, the combination of solar and wind turbines presented no issues with keeping the system charged, whereas during the winter period, when the power output from the solar panels falls to zero during the polar night, consistent power supply is more challenging due to the sole dependency on wind.

Solar power
There are two solar panels (facing south) and 2 solar panels on the roof for each container. The solar modules are a class of modules known as dual-string modules, with two parallel strings of cells, connected in the middle of the module. All solar panels are type REC Alpha Series, model 380 WP Power. The size of each panel is: 172.1 Â 101.6 Â 0.30 cm, weight: 19.5 kg. This type of module was chosen for both its high power and for its capability to resist shadow effects. It is expected that snow will pile up against the containers and thus shadow the vertically mounted modules. For dual-string modules the  vertically mounted modules perform at 50 % capacity when covered by snow up to 85-90 cm. deep, whereas a more commonly used layout of solar modules would see a power cut off entirely with snow coverage of < 20 cm. The solar modules are connected in serial per pair with one series being the vertically mounted modules and the other the two modules on the roof. The vertical solar modules are mounted with an aluminium insert system and the roof modules are mounted in an east/ west-system.

Wind power
The selected wind turbines, Superwind 353 from Superwind GmbH, mounted on a ø60 mm pole on the corner of the container, each have a power output of up to 350 W and dual bearings to resist the harsh and changing conditions they will be exposed to. The turbine has 3 carbon/glass fibre reinforced plastic blades and covers an area of 1.17 m 2 (diameter of 122 cm). The minimum space required for free turning (360°) is 126.3 cm. The cut in wind speed is 3.5 m/s with no upper limit. The nominal voltage is 24 VDC, and nominal power is 350 W at 12.5 m/s. The turbines have a ''dump off" of power that will serve as an occasional heat source in the container when batteries are fully charged as well as protection from excess wind conditions. This first setup has one wind turbine per container unit, but we will increase this to two in the next version to ensure sufficient power generation in over the dark winter period.

Power storage
The power storage consists of 14 lead-acid batteries with a rated capacity of 180 Ah/12 V (Fig. 5), resulting in a total capacity of 30 kWh. The size of each battery is 55.1 Â 12.5 Â 30.5 cm and weigh 64.4 kg. The batteries supply the power for the monitoring equipment and are equipped with a shunt resistor to track the state of charge with this output entering a Victron Smart Battery Protect System that shuts down the system when it falls to a state of charge of approximately 40 % to not completely discharge batteries and thereby preserve longevity. The lead batteries are chosen for their well-established durability in diverse conditions (temperature range, discharge rate) and though more suitable technologies exist, lead batteries are a solid compromise between performance and cost. Specifically, Li-ion batteries will see a drop off in charge acceptance at sub-zero temperatures reaching a cut off at the temperatures this system commonly experiences. For stowing, a custom-made rack is designed that also serve as transport encasing while hoisting the batteries in with helicopter to desolate locations. Batteries are series connected in pairs to a system voltage of 24 V with the same output feeding into all power converters.

Transportation and setup of container units
The containers were transported to Greenland by a Danish Navy vessel and slung into place by helicopter. Onsite installation is done by a technical team.

Energy consumption (monthly).
An example of the monthly power consumption in two different configured container systems is shown in Fig. 6. Details are found in supplementary (Power_consumption.xlsx). Power intensive equipment is only powered on when needed, e.g. the satellite system, routers and antennae. Other sensors, like the camera system (having their own power system) and chambers are turned off in the wintertime to reduce power consumption. The system is flexible and can easily be configured to adapt to different needs and environments.

Wiring system
The wiring diagram of the ARC-MO unit is presented in Fig. 7. The supply system can be remotely monitored through the Cerbo GX datalogger that also has wireless data transfer capabilities.

Data collection
Data collection is divided into three compartments:

Atmosphere Land (including streams) Ocean
Atmosphere Instruments for measurements of climatology, meteorology and surface fluxes are installed on a 6-meter mast approximately 20 m from the container (Fig. 8). The mast consists of two 3-meter sections, Carl C model B450. It is an equilateral triangle, where each side of the mast section are 45 cm wide. The mast is installed on a triangular metal plate and supported by three 6 mm guywires and stakes dug into the ground. The mast is transported in 3 m sections and assembled on site. All equipment, including the two smaller container units, were fitted into a 20 ft container and shipped to Daneborg in Northeast Greenland. We used a helicopter to transport to the exact deployment locations in Daneborg and in Zackenberg (25 km apart).

Ambient relative humidity and air temperature
The ambient relative humidity and air temperature is measured with a HMP155 Humidity and Temperature probe manufactured by Vaisala Oyj, Finland. The scaling for the relative humidity is 0 to 100 %, and for the temperature À80 to + 60°C. Both channels have an output of 0 to 1 V. The probe is mounted directly on the vertical leg on the mast in a Vaisala DTR503 radiation shield. The measuring hight is 5.2 m above ground.

Skin temperature
The skin temperature is measured with an Infrared Radiometer, model SI-100-SS manufactured by Apogee Instruments, Utah, USA. The sensor has an operation temperature of À55 to + 80°C, 0 to 100 % RH. Analog output is 0 to 2500 mV. The sensor is mounted on top of the mast (6 m above ground) in an angle to measure the skin temperature of the fjord.

PAR (Photosynthetically active Radiation)
PAR is measured with Quantum Sensor, model LI-190/R from Li-Cor Bioscience, Nebraska, USA. Operating temperature for this sensor is À40 to + 65°C. Output is 7 lA/1000 lmol s À1 m À2 . The PAR sensor is mounted on the mast at 6 m height above ground on a ø50 mm aluminium-boom pointing towards east.

Net radiation
Net radiation is measured with a Net Radiometer model NR Lite 2 manufactured by Kipp & Zonen B.V., The Netherlands.
The spectral range is 0.2 to 100 lm, and the operating temperature is À40 to + 80°C. The output is a low-level voltage output ranging from 0 to 15 mV. The sensor is mounted as an extension of a ø50 mm aluminium boom approximately 1.3 m away from the mast and at 6 m height above ground.

Global radiation
The global radiation is measured with a CMP 10 pyranometer manufactured by Kipp & Zonen B.V., The Netherlands. The spectral range is 285 to 2800 lm, and the operating temperature is À40 to + 80°C. Signal output is 0 to 20 mV. The global radiation sensor is installed at the mast on a ø50 mm aluminium-boom at 6 m height.

Data logging of meteorological parameters
All radiation instruments, temperature and humidity sensors are connected to a Campbell datalogger, model CR1000X for continuous data collection. The datalogger is connected to a server in the marine container with an approximately 28 m long cable.

Wind speed and direction, momentum fluxes and sensible heat fluxes
The 3-D wind components and temperature are measured at high frequency (10 Hz) with an ultrasonic anemometer Model uSonic-3 Scientific manufactured by METEK Meteorologische Messtechnik GmbH, Germany. The sensor head and the electronics are separated, and the anemometer is equipped with sensor head heating which can be turned on/off. It has analogue as well as digital data output (0 to 5 VDC & RS422), and in this setup the analogue output is used for data transmission. The parameter settings are: u: À60 to + 60 m s À1 , v: À60 to + 60 m s À1 , w: À5 to + 5 m s À1 , T: À50 to + 50°C. The ultrasonic anemometer is mounted at the end of a ø50 mm aluminium-boom in the mast at 6 m height, and the boom pointing towards the fjord (towards west).

CO 2 and latent heat fluxes
A LI-7200/RS Enclosed CO 2 /H 2 O gas analyzer is used in connection with a LI-7200-101 Flow Module and a heated inlet to measure fluxes of H 2 O and CO 2 . The system is manufactured by Li-Cor Bioscience, Nebraska, USA. The calibration range for CO 2 is 0 to 3000 lmol mol À1 , and for H 2 O 0 to 60 lmol mol À1 . The operation temperature is À25 to + 50°C. The output is 0 to 5 V and the power consumption is max. 37 W during warm-up, and 8 to 18 W steady state. The CO 2 /H 2 O sensor is installed in the mast at 6 m height. The sensor inlet is pointing towards the fjord (towards west) along the 50 mm aluminium-boom containing the ultrasonic anemometer. The LI-7200-101 Flow Module is mounted at the mast in 2.5 m height.

CH 4 fluxes
A LI-7700 Open Path CH 4 gas analyzer, manufactured by Li-Cor Bioscience, Nebraska, USA, is used to measure fluxes of CH 4 . The calibration range for CH 4 is 0 to 40 ppm @ +25°C, and 0 t0 25 ppm @ À25°C. The operation temperature is À25 to + 50°C. The output is 0 t0 5 V. Power consumption is 8 W nominally. The CH 4 sensor is installed on a ø50 mm aluminium-boom pointing towards south in the mast at 6 m height.

Data collection of heat, CO 2 and CH 4 fluxes
The uSonic-3 Scientific, the LI-7200/RS and the LI-7700 are connected to a LI-7550 Analyzer Interface Unit manufactured by Li-Cor Bioscience, Nebraska, USA for setup control and data collection. The LI-7550 has a 4 GB removable USB storage, an ethernet connection, RS-232 (57.600 baud, 20 records s À1 ) and 6 Digital-to-Analog converters (0-5 V). The operation temperature is À25 to + 50°C. Power consumption is 10 W nominally. The LI-7550 AIU is mounted at the mast in 2.5 m height.

Land
The terrestrial component for measuring GHG gas and energy exchange is based on two different techniques: eddy covariance (EC) (Fig. 9) and a modified version of an established automatic chamber (AC) setup (Fig. 10). The EC system is based on commercial, low power consuming CPEC306 developed by Campbell Scientific, equipped with a fast gas analyser (EC155) and sonic anemometer (CSAT3HCBL1) with a heating option installed on a stainless-steel tripod at 2.12 m height. The system operation and data collection is performed by a CR6 data logger (Campbell Sci.) which also acquires peripheral parameters such as solar radiation, air and soil parameters. Instruments measuring solar radiation are mounted on horizontal cross-boom attached to stainless steel tripod at 2.8 m height. The following spectrum of solar radiation is measured: global radiation-CMP10 pyranometer (Kipp&Zonnen), net radiation -NR-LITE2 (Kipp&Zonnen) and photosynthetically active radiation (PAR) with set of two quantum sensors -Li-190 (Li-Cor), one oriented downwards (reflected PAR) and second oriented upwards (incoming PAR). Apart from the radiation instruments the cross-boom also accommodates ultrasonic range sensor for snow depth measurements SR50 (Campbel Sci.). Air temperature and relative humidity is measured by HMP155A probe (Vaisala) -installation height 2 m. The EC tripod also accommodates a surface IR thermometer SI/111 (Apogee)installation height 1.5 m. In addition, 5 m away from the EC mast a simple tipping bucket TE525MM (Texas) connected to CR6 logger is installed for measuring rain precipitation. The EC system is also equipped with three independent soil profiles consisting of a set of two sensors: averaging soil temperature probe TCAV (Campbel Sci.) and self-calibrating soil heat flux plate HFP01SC (Huxeflux Thermal Sensors) each. The soil profiles are distributed in a radius of 10 m from the EC setup and represent main surrounding surface biomes, barren ground, grass and shrub characteristic for the location. The EC system clock is controlled and adjusted by GPS (Garmin). The fast EC data are collected in 10 Hz resolution (high frequency HF) and logger perform initial flux computation by averaging each 30 min of data and combining them with representative low frequency -30 min averages (LF) of radiation, air and soil parameters acquired simultaneously. CPEC306 system is connected by ethernet cable with local computer located inside the container which collect data and sends a daily report to the server via Iridium connection.
A typical automatic chamber (AC) setup consists of 10 chambers custom-made from aluminium alloy V-Slot 2020 profiles (RatRig, Portugal) and transparent Polycarbonate (3 mm thickness on walls, 6 mm thickness on the lid). This solution allows transportation in a compact dismounted state and for easy mounting in the field. The standard chamber size is 60 Â 60 cm and 50 cm high, however different sizes can be produced on the same principle. Chambers are operated by pneumatic pistons (SMC, CD85N20-250C-B) driven by a 24 V DC air compressor (STXOF7-6-24, Dankompressor, Denmark with EMD 12C 24VDC automatic drain) with working pressure 3 Bar in the pneumatic line. Sample air from the chambers is sucked through HDPE tubing (6 mm outer diameter, Eaton, Ireland) to the container where it is analysed by LI-7810 CH 4 /CO 2 /H 2 O Trace Gas Analyzer (Li-Cor Bioscience, Nebraska, USA). For the protection of the instrument, a water trap and a custom-made protection unit are set up before the analyser. The protection unit reacts on liquid water in the gas line (flood protection) and low pressure (clog protection) and switch the emergency valve to ensure the instrument keeps operational. The chamber operations are controlled by the same local computer (Lenovo T550) as the rest of the system. Depending on the distance between the container and the chambers, the communications can be realized by cables, Wi-Fi or LoRa.

Camera system
The camera system monitors plants and insects during the summer period approximately 500 m away from the terrestrial container (Zackenberg) and is supplied by its own solar power system. Two camera system are installed with a total of 8 (4 per system) nadir-facing camera designed for local-scale (<1 m 2 extent) plant and insect monitoring. A separate powered camera system with two oblique-facing cameras is located with view over the nearby brook to monitor ice melting. A leadacid battery with capacity of 100 Ah/12 V, a 12 V battery charger and two 60 W solar panels powers the camera system. ( Fig. 11). A computer (Arduino Nano) inside a custom-built battery controller turns the power on to the Wi-Fi Bridge and camera system in the period May 15 to August 31. The Wi-Fi Bridge and camera system each consume only 12 V/7 mA during the winter period, which is a sufficiently low consumption for the battery to survive an entire year without being charged.
The battery controller has a real time clock and performs timestamp logging of temperature, humidity, charge, and battery voltage every 30 min on a SD card inside the battery controller. The battery controller also ensures that the charger does not drain the battery when there is no sun during the winter period. A 5 V power supply is turned on during the summer period to power two Raspberry Pi Zero W (Wireless) computers that each are connected to two web cameras (Logitech C922 Pro Stream 1080p). The cameras capture images in the period from 8:00 AM to 8:00 PM with a time-lapse of 60 s. Images are stored with a backup of the last 10 weeks on a Micro SD card (32 GB) inside the Raspberry Pi Zero computer. The daily captured images are also transferred every afternoon between 9:00 PM to 11:00 PM to the FTP server in the terrestrial container.
The Raspberry Pi Zero W computers connects to the Wi-Fi Bridge (Fig. 12) that establishes long distance connection to the terrestrial container The Wi-Fi Bridge is powered by its own solar panel, battery and charger that are similar to the devices used for the camera system. The battery controller supplies 24 V to the TP Link CPE 210 that is configured as a Wi-Fi bridge and routes communication between the camera systems and terrestrial container.  Limnic Data collection in streams, rivers and lakes makes up another part of the terrestrial system. The measurements are divided into two parts: 1) whole-year data collection, and 2) additional data collection in open-water season. Parameters included in whole-year data collection are determined by which available sensors are able to withstand being frozen into water. These include water temperature (TinyTag; Gemini data loggers UK), light intensity (HOBO instruments, USA), specific conductivity (HOBO instruments, US), dissolved oxygen (DO; miniDOT, PME instruments, USA) and level logger transducer (Solinst, Canada). Freezing resistance of HOBO, PME and Solinst instruments are currently being tested.
At selected sites we include measurements of water dissolved organic carbon (DOC), turbidity and NO 3 by multi-sensor sondes (e.g. YSI, USA or S:CAN, Austria) during the open-water season. These multi-sensor sondes are unlikely to withstand in-freezing in the water during winter, and this data collection therefore requires at least two annual visits to the monitoring site. No lake or large river site is yet included in the monitoring.
In addition to measuring water chemistry, we install two cameras near the stream with one facing over the stream reach and one facing vertically into the stream water. Power supply and data transmission to and from camera and multi-sensor sondes is like the systems described for the plant and insect camera systems above.

Ocean cabled observatory
The ocean cabled observatory consists of an inductive link and sensors, an anchor, acoustic release, dyneema lines and buoyancy floats. The inductive link has a topside and subsea inductive modem (Develogic) interlinked with an inductive cable (horizontal length: 1 km, vertical: 16 m) and a swivel. The interfaced sensors, connected to the subsea inductive modem are a multiparameter ocean sensor and an acoustic doppler current profiler (ADCP) (Fig. 13).
The subsea unit consist of a data logger with inductive modem, internal battery pack (12 D cell lithium), magnetic power switch with status indicator and battery monitoring, a safety valve and 3 ports for sensors interfacing. The hard anodized aluminium housing of the subsea unit is rated for deployments up to 500 m depth.
The topside consists of a data logger with inductive communication interface and backup iridium modem. The combination of the topside and subsea unit allows for bidirectional transmission of data and configuration commands.
The inductive link consists of a 4 mm steel cable extruded to 6 mm with yellow polypropylene (PP) plastic and a breaking strength 9.5kN. The cable ends are terminated by titanium terminals that function as seawater electrodes for the inductive link. The vertical part of the cable is linked with the horizontal line on the seafloor via a titanium swivel with conductive feed through. The swivel has a 15 kN safe operating load and is suitable for both inductive and wired mooring setup.
Various instrumentation can be attached to the inductive link. In the present setup we selected a Nortek Signature 500 kHz ADCP instrument deployed in a protective buoy for telemetering hourly averaged velocity profiles and for 12 hourly derived ice keel and drift measurements. The RBRconcerto CTD instrument was selected for conductivity, temperature, and depth (pressure) recordings and it was furthermore equipped with a Turner fluorometer for Chlorophyll determination and a LI-COR PAR sensor for irradiance measurements. Both sensors are streaming serial data to the subsea unit which forwards the data to the topside unit where it is stored until the topside unit is interrogated by the container telemetry software for data submission to the servers.
The mooring setup further consists out of a 200 kg steel H-bar connected to an acoustic release (Edgetech Port LF) and 2 trawler beats (1 Â 3.2 kg + 1 Â 8.4 kg) which functions as buoyancy. The nodes are connected via dyneema lines of 7.95 mm (5/16 in.).

Deployment of cable 1 km out to 50 m depth
The cabled observatory was installed in a seasonally ice-covered fjord (Young Sound in NE Greenland, 74°21 N, 20°21 W) (Fig. 14). To protect the cable against scouring effect of sea ice and icebergs the first 25 m of the cable was protected by polyethylene (PE) pipes welded together via electrolysis. During lowest low water, a trench was dug to bury the PE pipes and cable in the sediment to further prevent the effect of ice on shore landing of the cable. We were fortunate to borrow a digger from the Sirius Dog Sled Patrol, but the work can also be done by hand, making it possible to install units in remote areas with helicopter access only. The spool with 1 km cable was loaded on a 6 m support vessel and unwinded to the deployment area, where the mooring was anchored on the seafloor. The releaser attached to the anchor allow for an acoustic release of the mooring line when the mooring is to be inspected or instruments replaced each year or second year with new calibrated sensors and charged batteries.

Data storage and transmission
The atmospheric and terrestrial data from the ARC-MO units are collected directly on a CR6 datalogger equipped with 16 GB industrial grade microSD memory card. The ocean data is stored on the topside unit. Daily, all data are synchronized with a local computer (Lenovo T 550) located inside the container (Fig. 15). HF data are collected via ftp protocol directly from logger memory card and LF data are synchronized with the use of LoggerNet software with a build-in schedule collection feature. All data are saved and stored on the internal HDD of the Lenovo T550 computer. The local computer initiates Iridium connection on daily basis and transmit single a LF data file to data server.

Server
A Lenovo T 550 computer is used for data handling, FTP-and application server in both containers (Marine, Terrestrial). This model has standard operating specifications suitable for work in extreme environments (low temperature, high humidity, low power consumption). It is also designed to restart after an optionally power failure. Both average data and high frequency data from the data loggers and camera system is stored on a 2 Tb SSD hard disk.

Data transmission
In both containers, the server runs a scheduled job for transmitting data by the Iridium satellite system (Iridium Sailor 4300) (Fig. 15). The job turns on a relay to power up the Iridium modem, compress data files, waits until an internet connection is established, then transmit data by FTP. The connection is then closed, and the modem powered off. The data files are currently transmitted to a FTP server at Aarhus University. If the connection is not established and/or data files are not transmitted successfully, the computer will retry to send the data files later. It is also an option to access the station by an external FTP connection and download data or upload new applications or setup files (via static IP address and using port forwarding). Only averaged result files and status files are sent, currently below 100 Kb each day. The max transfer speed is 172 Kb/s. Raw files (high frequency data etc.) and pictures from the camera system are saved on the hard disk (and on the Campbell data loggers as long as space is available). To keep telemetry costs acceptable, these files need to be collected when visiting the station.

Wi-Fi connection
Between the two containers, Ubiquiti Rockets (Prism 5AC 5 GHz) and Ubiquiti airMax disk antennas establish a data link via a long range Wi-Fi connection (Fig. 15). The distance between the two containers is 25 km. Moreover, it is possible to transmit data within the stations. More specifically, between the terrestrial container (Zackenberg) and the camera system and the limnic sites. There, a TP Link CPE 210 establishes the Wi-Fi connection. We selected a 2.4 GHz system, because the Raspberry Pi computers also connect by Wi-Fi, and do not support 5 GHz. The camera system is only running in the summertime (from May 1. to August 31.). For the rest of the year, the Wi-Fi system is turned off.

Data access
The data stored on the FTP server is automatically transferred via a downloading script running on a local server to a local PostgreSQL database (Fig. 16). There, a processing script generates derived values from the measurements to calculate parameters such as sea ice thickness and status of the system and system components. The database is then linked with a Grafana dashboard to visualize selected measurements, derived values, and health parameters from the system. Each link of this chain is deployed locally on the server via a Docker container, which allows the installation to be reproducible and scalable. The coding is done in the Python programming environment, which makes it easy to read and reusable by a large community of users.
The Grafana dashboard allows to dynamically change the time range of visualization and to have an overview of all the available data (Fig. 17). We use a combination of standard plotting tools and custom plugins (plotly, Grafana Labs) in the Grafana dashboard to display both time series data and profile data of the acoustic doppler current profiler (ADCP). Visual links between different data plots can be made through a duplicated cursor shown on all the graphs. Furthermore, Grafana allows to generate alerts based on the received data, which allows users to be notified by changing status of the system or by environmental changes detected by the sensors.
All displayed data (raw, filtered and derived data) can be downloaded directly through the application in csv format. This comprises both the raw data generated by the sensors, the filtered data and the derived data. Data tiles can be shared via links, snapshots and embedded via an automatically generated html code.
The data is available on our Greenland Integrated Observing System (GIOS) homepage https://gios.org.

Price
The cost of the various components of ARC-MO is presented in Fig. 18. The central hub containing solar panel, windmill, batteries, wiring system and server systems accounts for 9 % of the total cost, the other units, e.g. atmosphere, land, limnic and ocean can be combined as desired. The cost for a full system covering atmosphere, land and ocean is 304.000 €. A detailed Bill Of Material (BOM) file can be found in design file (BOM.xlsx).

Design files summary
The design files for the ARC-MO are organized into five different components: (1) the central hub connecting the different measuring units in the (2) atmosphere, (3) on land, (4) lakes & streams and (5) the ocean (Fig. 19).

Build instructions
The building instructions for the ARC-MO is organized into 5 components according to Fig. 19  box on the mast. On the Atmospheric, use an Ethernet switch to collect Ethernet cables (the distance between the mast and container must not exceed 100 m). Connect an Ethernet cable and route it together power cables into the container thought ventilation openings. Encapsulate all cables going from the mast into the container in protective piping. Inside the container attach the power cables and connect the Ethernet cable in the switch on the wall.

Power
(1.03_01) Batteries are placed in the transport cage and transported to the container unit. Remove the sidewalls from the battery cage. Organize batteries in 2 layers with a wood placeholder between the batteries for the cables. The top plate is replaced to protect the batteries and serve as a working bench for the server. Connect batteries to the wiring system upon arrival at the field location.
2. Atmosphere 2.01. Mast set up Á (2.01_1) Find a solid flat ground of a suitable size or make a foundation both depending on the surface for the mast 45 cm triangular guyed mast incl. bottom plate. Á Install three spears or eyebolts of a suitable size in the ground of each of the corners of the mast depending on the surface in a distance away from the mast according to standard. (approx. same distance away from the mast as the distance from the ground to the point where the guy wires are attached to the mast.). We have been using a detachment point approx. ⅔ up the tower. Á Attach the three 6-8 mm guy wire to the mast, one in each corner of the mast, using suitable Eureka wire locks (2.01_02) (or other brands). Á Raise the mast on the flat ground or on the foundation. Á Fasten each of the wires attached to the corners of the mast to a turnbuckle using suitable Euraka wire locks, and attach the turnbuckle to each of the spears/eyebolts Á Tighten the wires so the mast is stable (do not over tighten the wires), and safe to climb. Á Drill 4 holes in a straight line with a distance of 50 cm, starting approx. 5 cm from one end, and one hole in the opposite end in two 3 m long, ø50 mm aluminum booms in order to be able to install various types of equipment. Á Install two mast clamps (2.01_03) for each of the aluminum booms in the chosen height, and level them horizontally. Á One boom should point towards the water (mounted on the side of the mast, which is 90 deg of the coastline), and one should be pointing against the prevailing wind direction mounted on the side of the mast facing the water. Á Make sure the pre-drilled holes in the booms are pointing towards the water for one boom and towards the prevailing wind direction for the other one.

Meteorology
Á (2.02_2 & 2.02_3) Install the ultrasonic anemometer at the hole at the end of the boom (hole 1) pointing towards the water. Á Install the ultrasonic anemometer electronics box directly to the mast an approximately 3.5 m height and connect the sensor. Á Install a PAR sensor at the end pointing opposite the ultrasonic anemometer. Á Mount the skin temperature sensor on the ''LI-7700 CH 4 sensor boom" just outside the mast and point the skin temperature sensor at a point always a of the coast the in the water. Opposite the LI-7700 CH 4 sensor the global radiation sensor must be installed on the boom, and the net radiation sensor must be installed further away on its own boom. Á The temperature/rel. humidity probe can be installed directly to the mast a little below the boom arrangement. Á Connect all instruments to the DAQ cabinet and connect the cabinet to the container. Á All instruments are connected using Burndy plugs, where female pins are mounted in the cabinet (2.04_01), and the instrument cables are fitted with male pins (2.04_2). Á All cables and the tubing for all instruments must be fastened closely to the booms and down one leg of the mast. Á Excessive cables must be coil up and fastened to the mast at approx. 3 m height. Á All cables running to/from the container are protected by a heavy cable conduct on the ground and a ø50 mm aluminum boom section from the ground to the DAQ cabinet due to wildlife. Á We are using vinyl electrical tape (Scotch Super 88) for fastening cables and tubing.
3. Land 3.01. Soil (3.01_01) Make three $ 20 cm deep soil openings with shovel (in our case $ 9 m away from the EC tower -maximal distance allowed by sensor cable length). Insert soil temperature sensors at À0.5, À5.5, À10.5 and À15.5 cm depth in one vertical line and insert soil heat flux plate sensor into suitable soil pocket at the depth of À16.0 cm (important to insert the probe plate in correct orientation indicated on the sensor). Fill the opening with extruded soil making sure buried sensors have proper contact with soil. In areas where wildlife interaction likelihood is high it is recommended to protect the cables with robust cable conducts. Connect sensors to CR6 logger.
3.02. Precipitation (3.02_01) Mount rain gauge on the separate 1 m tall pole in some distance from the mast (in our case $ 7 m West). Since this sensor is relatively light, a solution with simple pole inserted directly into the ground was sufficient in our case. In areas where wildlife interaction likelihood is high it is recommended to protect the cables with robust cable conducts.
3.03. Fluxes air meteorology and radiation sensors (3.03_01) Unfold the stainless steel tripod some distance from the container (in our case 20 m East -limited by the length of both power and ethernet cable). Adjust tripod legs to make sure the central tripod pole is vertical. Mount EC system enclosures (logger with pump, anemometer electronic box -EC100, as well as anemometer heating control unit) accord-ing to manufacturer instructions. Install GPS and global radiation sensor at the top of the centre pole with use of provided mounts. Install cross boom for other radiation sensors (should be installed as high as possible and oriented along North-South direction). On southern end of radiation cross boom install net radiometer (suitable mount is provided by manufacturer) as well as 2xPAR sensors. On the northern end of radiation sensor install snow range sensor. Install anemometer and gas analyser cross boom. To minimize the construction influence on eddy covariance measurements anemometer and gas analyser cross boom should be oriented perpendicular to main wind direction specific for the site (in our case 86°, N for main wind direction NAS). Finally, install air temperature and surface temperature sensors on the main pole of the tripod with mounts provided by manufacturer.
3.04. Camera system for recording nadir photos at high temporal frequency (3.04_1) This sensor system consists of power supply units, camera units and a WiFi bridge connecting the sensors to the terrestrial container. Camera units are mounted on a rack built from aluminium tubes assembled with K clamps. They must be positioned with a distance of c. 30 cm above the plants to record. The camera units connect to the Wi-Fi bridge, which again connects to the server in the container. The power supply units consist of two solar panels, a charge regulator, battery and battery controller (Fig. 12). The two solar panels should be connected in parallel to the input of the charge regulator. The output of the charge regulator is connected to the battery controller. The battery controller is connected to the lead-acid 12 V battery and supplies 5 V to the Raspberry Pi's with cameras. The power supply to either the camera units or the WiFi bridge is shut down by battery controllers during the winter period to ensure efficient power management, a period when solar panels are unable to deliver power to the batteries. e. Check all battery voltages; these must be within 1 % of each other. 6. Connect Display, here you will get an overview of the overall system. 7. With the VictronConnect app you will be able to communicate with all components via Bluetooth (Fig. 20).

Operations check of the system from remote
Data collection by the various sensors (atmosphere, land, ocean) and status can be monitored remotely via the Greenland Integrated Observing System (GIOS) homepage (https://gios.org) using the Grafana dashboard (Fig. 17). We are continuing to update information on the system health e.g. battery voltage, pitch and roll for ocean ADCP mooring, data transmission etc.

Concerning the server and communication
Check this out when visiting the field: 2. Check that all loggers (i.e. water temperature (TinyTag; Gemini data loggers UK), light intensity (HOBO instruments, USA), specific conductivity (HOBO instruments, US), dissolved oxygen (DO; miniDOT, PME instruments, USA) and level logger transducer (Solinst, Canada)). 3. Upload data from the loggers, replace batteries where relevant, and re-position the loggers in the same positions. 4. Check for loose cables and the mounting systems from solar panels to battery, and from battery to multi-sensor sondes. 5. Upload data and replace batteries if relevant. At the end of the season, bring back the multi-sensor sonde to laboratory. 6. For cameras, follow the list from 1 to 8 above (Safety instructions and maintenance of the time-lapse camera installation when visiting in the field).

Ocean
Safety instructions and maintenance of the ARC-MO (ocean unit) system when visiting in the field: 1. Check that all protective piping from the container to the sea are intact. 2. In case ocean sensors and/or batteries need replacement use standard ocean mooring procedures e.g., acoustic release the mooring instruments from the anchor, replace instrument with new calibrated sensors fully charged batteries on the inductive mooring line. 3. Inspect the inductive mooring line, buoyancy, and swivels for damage, wear and tear. 4. Connect a newly serviced releaser with fully charged batteries to a new anchor and lower it to the seafloor. Make sure not to damage the cable under operations. 5. Check connection to the ocean mooring in the central ARC-MO hub and ensure data is transmitted and health conditions are fine. 6. Ensure standard safety procedures are followed when operating at sea. 7. Download and backup data from instruments.

Validation and characterization
The extreme climate, the sparse infrastructure and the costly logistics make it challenging to work in the Arctic and to collect data year-round, especially during dark winter conditions. The new ARC-MO units will be an important asset to collect measurements across the landscape at times and locations where traditional logistics are prohibitively challenging. With an aim to eventually upscale long-term data collection (e.g. https://g-e-m.dk) to entire Greenland, our ARC-MO units to function as critical ground truth validation for ongoing and future satellite upscaling. An important next step in this approach will be the placement of ARC-MO units from South Greenland (60°N) to North Greenland (81°N) along climatic gradients. As the temperature gradients over a 100 km west to east section from the ocean to the Greenland ice sheet can be as steep as the temperature difference over a 2700 km south to north section, we plan to place units from the Greenland ice sheet to the outer coast (east-west) as well. This will provide a novel study approach covering both spatial and temporal variability. The ARC-MO units will be central in the Greenland Integrating Observing System (GIOS, https://gios.org).
Capabilities (and limitations) of the ARC-MO hardware Capable of operating under harsh Arctic conditions. Capable of autonomous data collection from air, land, rivers and ocean. Capable of transferring near real-time data. Flexible system allowing for different sensor packages. A limiting factor for the hardware is the power production during the dark winter months where solar panels do not function and where units rely on power generation from the windmill and internal batteries. A limiting factor for the real-time data transfer is the cost. At present we are not transmitting large size files, e.g. photos, and all instruments' raw data. These must be collected on the annual service visit to the units.

Future improvements
Due to very poor sea ice conditions during deployment unusual high numbers of polar bears were observed in the area. Besides very close encounters between polar bears and scientists (luckily without severe injuries for bear and scientists) this resulted in polar bear damage on some cables and instruments. We are working on an improved ways to protect our instruments from polar bears. In the present setup, cables running on ground from the container to mast/instruments were all protected by ''armored hose" or ''steel enforced hose". These have proven successful for smaller wildlife such as foxes and muskoxen. We also need to increase battery capacity in our sub-sea inductive mooring as low temperatures under Arctic conditions are reducing battery capacity more than expected for this system. New satellite systems and reduced data transmission costs and power usage (e.g. STARLINK or Swarm) open up the possibility for transmitting raw data in near real time.

Ethics statements
Not relevant.

Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.